A gas turbine may be incorporated in a combined cycle power plant. As the name suggests, a typical combined cycle power plant combines two or more thermal cycles within a single power plant. There are normally two cycles in a combined cycle power plant classified as “topping” and “bottoming” cycles. Most or all heat is supplied in the topping cycle. The waste heat produced in the topping cycle is utilized in the bottoming cycle, which operates at a lower temperature level than the topping cycle.
Generally, a combined cycle power plant includes a gas turbine, a steam turbine, a heat recovery steam generator, a performance heater and a fuel moisturizer. Dry fuel gas enters the system in the fuel moisturizer, where the fuel gas is moisturized with water before entering the performance heater. After being superheated, the moist fuel gas enters the gas turbine system for combustion. The effluents from the combustion reaction expand in the gas turbine driving a rotor coupled to a load, e.g., to generate electricity. The exhaust from the gas turbine enters the heat recovery steam generator, which utilizes the heat from the gas turbine exhaust to generate steam for use in the steam turbine. The steam generated in the heat recovery steam generator expands in the steam turbine generating additional power.
Fuel moisturization can improve overall combined cycle performance of the power plant. When fuel is moisturized, the fuel properties do change, which in turn have an effect on the operations of the gas turbine.